This invention relates to organoborane amine complexes that are useful as free radical polymerization initiators. In another embodiment, this invention relates to polymerizable compositions comprising compounds containing moieties capable of free radical polymerization and organoborane amine complex initiators of the invention. In yet another embodiment the invention relates to adhesive, sealant, coating and ink compositions containing organoborane amine complexes and compounds containing moieties capable of free radical polymerization.
In many practical situations in which compounds are subjected to polymerization or where adhesives are used, it is desirable to have polymerizable compositions and adhesive compositions which can cure on demand. Cure on demand means that the polymerization can be initiated when desired. A significant problem with cure on demand compositions is the stability of the compositions. Many such compositions will begin curing at, or near, ambient temperature or will partially cure at ambient temperature resulting in an increased viscosity causing difficulties in handling and reduced functionality of the polymerizable composition or adhesive composition.
Low surface energy olefins such as polyethylene, polypropylene and polytetrafluroethylene have a variety of attractive properties in a variety of uses, such as for toys, automobile parts, furniture applications and the like. Because of the low surface energy of these plastic materials, it is very difficult to find adhesive compositions which bond to these materials. The commercially available adhesives which are used for these plastics require time consuming or extensive pretreatment of the surface before the adhesive will bond to the surface. Such pretreatments include corona treatment, flame treatment and the like. The requirement for extensive pretreatment of the surface results in significant limitations to the designers of automobile components, toys, furniture and the like. What is needed is adhesive compositions which are capable of bonding to low surface energy substrates, and bonding low surface energy substrates to other substrates, without the need for extensive or costly pretreatment.
Mottus et al., U.S. Pat. No. 3,275,611 discloses a process for polymerizing olefinic compounds with a catalyst comprising an organoborane compound, a peroxygen compound and an amine. It is disclosed that the organoborane compound and amine may be added to the reaction mixture separately or as a preformed complex, and that the complex is preferred. The presence of the amine in the complex reduces the pyrophoricity of the organoborane in air. Among the amine complexing agents disclosed are pyridine, aniline, toluidine, dimethylbenzylamine, and nicotine. Many of the complexes disclosed in Mottus are pyrophoric at all amine to boron atom ratios. In addition, many of the amine complexes do not display significant adhesive properties when applied to low surface energy substrates.
A series of patents issued to Skoultchi (U.S. Pat. Nos. 5,106,928, 5,143,884, 5,286,821, 5,310,835 and 5,376,746) disclose a two-part initiator system that is reportedly useful in acrylic adhesive compositions. The first part of the two-part system includes a stable. organoborane-amine complex and the second part includes a destabilizer or activator such as an organic acid or an aldehyde. The organoborane compound of the complex has three ligands which can be selected from C1-10 alkyl groups or phenyl groups. Useful amines disclosed include octylamine, 1,6 diaminohexane, diethylamine, dibutylamine, diethylenetriamine, dipropylenediamine, 1,3 propylene diamine, and 1,2 propylene diamine. The adhesive compositions are disclosed to be useful in structural and semi-structural adhesive applications, such as speaker magnets, metal to metal bonding, automotive glass to metal bonding, glass to glass bonding, circuit board component bonding, bonding select plastics to metal, glass to wood, etc. and for electric motor magnets.
Zharov et al. discloses in a series of U.S. Pat. Nos. (U.S. Pat. No. 5,539,070; U.S. Pat. No. 5,690,780; and U.S. Pat. No. 5,691,065) polymerizable acrylic compositions which are particularly useful as adhesives wherein organoborane amine complexes are used to initiate cure. The organoboranes used have three ligands attached to the borane atom which are selected from C1-10 alkyl groups and phenyl. The amine is an alkanol amine or a diamine where the first amine group can be a primary or secondary amine and the second amine is a primary amine. It is disclosed that these complexes are good for initiating polymerization of an adhesive which bonds to low surface energy substrates.
Pocius in a series of patents (U.S. Pat. No. 5,616,796; U.S. Pat. No. 5,6211,43; U.S. Pat. No. 5,681,910; U.S. Pat. No. 5,686,544; U.S. Pat. No. 5,718,977; and U.S. Pat. No. 5,795,657) disclose amine organoborane complexes with a variety of amines such as polyoxyalkylene polyamines and polyamines which are the reaction product of diprimary amines and compound having at least two groups which react with a primary amine.
Many of the complexes disclosed in the Zharov, Skoultchi and Pocius Patents are not stable in compositions containing olefinic unsaturation at, or near, ambient temperatures and thus the complexes disassociate and induce polymerization at, or near, ambient temperature with time. This instability at, or near, ambient temperature can result in polymerization before desired and can result in compositions which are unsuitable for the desired use.
Therefore, there is a need for initiator systems for free radical polymerization which are safe to handle, not pyrophoric, which can be used to form cure on demand polymer systems or can be used in adhesive systems which cure on demand. What is further needed are adhesive systems which are capable of bonding to low surface energy substrates, and initiator systems which facilitate such bonding. In addition to such needs, the complexes need to be thermally stable, that is do not disassociate at, or near, ambient temperatures and thereby initiate polymerization before desired. What are further needed are polymer compositions and adhesive systems which are thermally stable at, or near, ambient temperatures and which will undergo polymerization when the user desires.
In one embodiment the invention is an amine organoborane complex wherein the organoborane is a trialkyl borane and the amine is selected from the group of amines having an amidine structural component; aliphatic heterocycles having at least one nitrogen in the heterocyclic ring wherein the heterocyclic compound may also contain one or more nitrogen atoms, oxygen atoms, sulfur atoms, or double bonds in the heterocycle; primary amines which in addition have one or more hydrogen bond accepting groups wherein there are at least two carbon atoms, preferably at least three carbon atoms, between the primary amine and the hydrogen bond accepting group, such that due to inter- or intramolecular interactions within the complex the strength of the Bxe2x80x94N bond is increased; and conjugated imines. Preferred hydrogen bond accepting groups include the following: primary amines, secondary amines, tertiary amines, ethers, halogens, polyethers or polyamines. Heterocycle as used herein refers to a compound having one or more aliphatic cyclic rings of which one of the rings contains nitrogen. The amidines or conjugated imines can be straight or branched chain or cyclic.
In another embodiment the invention comprises a polymerizable composition which comprises an amine organoborane complex of the invention and one or more of monomers, oligomers or polymers having olefinic unsaturation which are capable of polymerization by free radical polymerization. This composition can undergo polymerization by exposing the composition to temperatures at which the organoborane amine complex undergoes disassociation. In another embodiment the invention is a polymerizable composition which further comprises an effective amount of a compound which causes the complex to disassociate (decomplexing agent), thereby freeing the borane to initiate polymerization of the one or more monomers, oligomers or polymers having olefinic unsaturation. The compound which causes disassociation of the complex is kept separate from the complex until initiation of polymerization is desired. In yet another embodiment the invention is a method of polymerization comprising a contacting of the components of the polymerizable compositions under conditions that the one or more monomers, oligomers or polymers undergo polymerization. The polymerizable composition which contains the decomplexing agent can be cured at any desired temperature, such as at, or near, ambient temperature and below ambient temperature.
The polymerizable compositions of the invention can be used as adhesive, sealant, coating or ink compositions. In one embodiment two or more substrates are bonded together by contacting the components of the adhesive composition of the invention, including the decomplexing agent, together under conditions such that polymerization is initiated; contacting the adhesive composition with the two or more substrates; positioning the two or more substrates such that the adhesive composition is located between the two or more substrates wherein they are in contact with one another; and allowing the adhesive to cure so as to bond the two or more substrates together. The thermally curing compositions of the invention can be used to bond two or more substrates together by contacting the adhesive composition with the substrates such that the adhesive composition is located between the two or more substrates and exposing the adhesive composition to a temperature at which the complex disassociates and initiating the free radical polymerization of the monomer, oligomers, polymers or a mixture thereof.
The complexes of the invention are safe to handle, not pyrophoric, are stable at, or near, ambient temperature and therefore will not initiate polymerization at, or near, ambient temperature in the absence of an initiator that causes the complex to disassociate. The polymeric compositions of the invention are stable at, or near, ambient temperature and can be cured upon demand by contacting the complex with the compounds which cause disassociation of the complex, or alternatively by heating the polymeric compositions above the thermal disassociation temperature of the complex. Furthermore, the adhesive, sealant, coating and ink compositions of the invention can form good bonds to low surface energy substrates without the need for primers or surface treatment.